Direct view storage tube having a lateral field neutralizing electrode adjacent the storage grid

ABSTRACT

A transmission type direct storage tube in which a lateral field neutralizer electrode is positioned adjacent the transmission storage electrode to confine the lateral effects of charge on the storage electrode to individual mesh openings in the storage electrode and prevent interaction with neighboring mesh openings.

nite States atet 1 Ogland 1 Sept. 24, 1974 [54] DIRECT VIEW STORAGE TUBEHAVING A 3,302,054 1/1967 Courtan i 315/12 LATERAL FIELD NEUTRALIZING3,459,990 8/1969 Brooke et a1, 315/12 X 3,480,482 11/1969 Picker 315/12X ELECTRODE ADJACENT THE STORAGE GRID Inventor: Jon W. Ogland, GlenBurnie, Md.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: June 16, 1972 Appl. No; 263,561

Assignee:

References Cited UNITED STATES PATENTS 8/1965 Davis 315/12 X PULSE 45\49 PULSE SOURCE J SOURCE T Primary Examiner-Carl D. Quarforth AssistantExaminerP. A. Nelson Attorney, Agent, or Firm-W, G, Sutcliff [57]ABSTRACT A transmission type direct storage tube in which :1 lateralfield neutralizer electrode is positioned adjacent the transmissionstorage electrode to confine the lateral effects of charge on thestorage electrode to individual mesh openings in the storage electrodeand prevent interaction with neighboring mesh openings.

9 Claims, 8 Drawing Figures SIGNAL SOURCE Emma 39241914 COLLECTORELECTRON PA'BH A cHAEEED CHARGED TO- 12v PHOSPHOR SCREEN DIRECT VIEWSTORAGE TUBE HAVING A LATERAL FIELD NEUTRALIZING ELECTRODE ADJACENT THESTORAGE GRID BACKGROUND OF THE INVENTION The transmission type directview storage display tube provides significant improvement over aconventional cathode ray tube in that it provides means for viewing animage for a substantial length of time without degradation of the image.It has been found in these storage tubes that there is a loss ofresolution in the storage mesh. It is also found that the brightness ofsmall spots on the display such as a moving target, does not increaselinearly but logarithmically with deposited charge and saturates at alow level. It is found that a small target attains a much lowerbrightness than larger target on a radar screen. The number of shades ofgray is also greatly reduced. This deficiency is particularlydetrimental in that small spots or targets require higher brightnessthan larger spots for visual detection.

SUMMARY OF THE INVENTION A transmission type of direct view storage tubeis provided in which a lateral field neutralizing electrode is utilizedfor confining the charge field associated with a single aperture in thetransmission storage electrode to that aperture without affecting aneighboring aperture control.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of thisinvention, reference may be had to the preferred embodiment, exemplaryof the invention, shown in the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a direct view transmission type storagetube in accordance with the teachings of this invention;

FIG. 2 is an enlarged view of the storage assembly of FIG. 1;

FIG. 3 illustrates the brightness built up of an enlarged spot or areain a storage tube in comparison with the built up of a small spot in aprior art type structure;

FIG. 4 illustrates roughly the field pattern within the storage gridassembly of a prior art structure;

FIG. 5 illustrates the field configuration in a storage tube inaccordance with the teachings of this invention;

FIG. 6 is a perspective view of a modified storage target assembly thatmay be incorporated into FIG. 1;

FIG. 7 is a perspective view of another modified-stor age targetassembly that may be incorporated into FIG. 1; and

FIG. 8 is a sectional view of another modified storage target assemblythat may be incorporated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a directview transmission storage tube is shown. The tube comprises an evacuatedenvelope 10. The envelope 10 is comprised of a tubular body portion '14connected by a tapered portion 16 to a tubular neck portion 18 ofsmaller diameter than the tubular body portion '14. The body portion 14is closed at its other end by a face plate portion 20 of a suitableradiation transmissive material such as glass.

The other end of the neck portion 18 is closed by a suitable baseportion 19 containing lead-in members (not shown) for applying voltagesto the electrodes provided within the envelope 10.

An electron sensitive coating 22 is provided on the inner surface of theface plate 20. The electron sensitive coating 22 is a display screen andmay be of a suitable phosphor material which emits visible light inresponse to electron bombardment. A suitable phosphor material is zincsulfide. The phosphor coating 22 is also provided with an electricallyconductive coating 26 of a suitable material such as aluminum. A lead-in28 is provided to the exterior of the envelope 10 from the electricallyconductive coating 26 and is connected to a suitable potential source15. The potential applied to the conductive coating 26 may be about10,000 volts positive with respect to ground.

Disposed adjacent to the phosphor screen 22 is a suppressor electrode24. The suppressor electrode 24 may be positioned at a distance of aboutone-eighth inch from the screen 22. The suppressor electrode 24 may beof a suitable electrical conductive material such as nickel which isformed into an electroform mesh with about 500 lines per inch. Thesuppressor electrode 26 may be connected by a lead-in member 23 to asuitable potential source 35. The potential source 35 may be of apotential of about volts with respect to ground. A voltage source 55 mayalso be connected to the lead-in member 23 to provide operation of theelectrode 24 in the manner set forth in US. Pat. No. 3,088,048 by Oglandet al.

A storage grid 30 is disposed adjacent-to the suppressor grid 24 and onthe opposite side thereof with respect to the screen 22. The storageelectrode 30 is comprised of a mesh 29 of a suitableelectricallyconductive material such as nickel having about 500 linesper inch. The mesh 29 is provided with a coating 31 thereon suitableinsulating material such as magnesium fluoride. Other suitable materialsare silicon monoxide, calcium floride, and aluminum oxide. This coating31 is disposed on the side of the mesh 29 remote with respect to thescreen 22. It may have a thickness of about 2 micrometers. The storagegrid 30 is disposed at a distance of about 0.01 to 0.03 inch from thesuppressor electrode 24. The storage grid 30 is also connected to asuitable vpotential source 41 by means of a lead-in 13. The potentialsource 41 may provide a potential of about 15 volts with respecttoground. Again, a voltage source 53 maybe connected to the lead-in 13 topermit erasure in a manner set forth in US. Pat. No. 3,088,048.

A'field neutralizing mesh 40 is disposed on'the opposite side of thestorage grid 30 with respect to the screen 22. The field neutralizingmesh 40 is positioned at a distance of .about 0.002 inch from thestorage grid 30. Here again, the field neutralizing electrode 40 may beof electrical conductive material such as nickel having about 500 linesper .inch. The field neutralizing electrode 40 is connected by a lead-inmember 42to a suitable potential source 45. The vpotential source 45 mayprovide a potential of about 5 volts with respect to ground.

A collector mesh 47 is disposed on the opposite side of the fieldneutralizing mesh 40 with respect to the screen 22. The collector-mesh47 is positioned at a distance of about'0.2 inch fromthe fieldneutralizing mesh 40. The collector mesh 47 is of an electricalconductive material such as nickel having about 500 lines per inch. Thecollector mesh 47 is connected by a lead-in member 43 to a suitablepotential source 49. The potential source 49 may provide a potential ofabout 250 volts with respect to ground.

A writing electron gun 50 is positioned within the neck portion 18 forgenerating and directing an electron beam onto the storage grid 30. Theelectron gun 50 generates a pencil-like electron beam of a small spotsize. The electron gun 50 may be of any suitable construction to providesuch a beam and comprises at least a cathode 52 and a control grid 54.The cathode 52 may be connected to the negative terminal of a suitablepotential source 51 of about 2,000 volts with the positive terminalconnected to ground. The control grid 54 is connected to an input signalsource 57 with a suitable bias as illustrated. Horizontal and verticaldeflection plates 56 and 58 are provided for deflecting the electronbeam from the electron gun 50 over the storage grid 30. Suitabledeflection voltages are applied to the deflection plates 56 and 58 toscan the writing electron beam from the electron gun 50, over thestorage grid 30. Alternatively, a magnetic yoke may be applied toprovide electromagnetic deflection of the electron beam.

Also positioned within the neck portion 18 of the envelope is a secondelectron gun assembly 60 which may be referred to as a viewing orreading gun and it performs the function of reading and erasinginformation on the storage grid 30. The reading electron gun 60 providesa large area beam so as to substantially flood the entire area of thestorage mesh 30. The flood gun 60 includes at least a cathode 62 and acontrol grid 64. The cathode 62 may be connected to ground potential. Awall coating 66 extends from just in front of the electron gun 60 tonear the collector grid 47. The wall coating 66 is connected to asuitable potential source 68 and is operated at a potential of about 70volts positive with respect to ground. The wall coating 66 is anelectrically conducting coating of a suitable material such as aquadagand is normally referred to as a collimating electrode for directing theflooding electron beams onto the storage grid so that the electronsapproach substantially normal to the surface of the storage grid 30.

In the normal operation of a device prior to the writing operation, thestorage grid 30 and the back plate or backing electrode 29 may be pulsedto a potential of about 20 volts positive with respect to ground bymeans of the potential source 53. The field neutralizing electrode 40may be at a potential of about 5 volts. The flooding electron gun 60will direct electrons onto the dielectric storage surface 31 causing thesurface to charge to a potential of about ground. The potentialdifference across the dielectric at this time is about 20 volts. It isalso customary in the operation of this device to pulse the suppressorelectrode 24 to a negative potential of about 80 volts by the source 55in order to prevent any electrons passing through to the phosphor screen22 during the erase cycle. On removal of erase pulse, the electrode 29will return to a positive potential of about l5 volts. The electrode 40will be returned to a potential of about 5 volts. The charge stored onthe dielectric surface 30 changes from ground potential to a negativepotential approximately equal to about 5 volts negative with respect toground due to capacitive coupling. This voltage is normally adequate tocut off the tube.

During the writing operation, the electron gun is modulated by thesignal from the signal source 57 and generates a small pencil typeelectron beam which is deflected over the storage grid 30 by means ofthe deflection plates 56 and 58. The cathode 52 of the writing gun 50 isgenerally operated at a potential of about L500 to 2,500 volts negativewith respect to ground. The signal source 57 modulates the control grid54 of the writing gun 50 in accordance with the information to bewritten onto the storage grid 30. The collector grid 47 is operated at apositive potential of about 250 volts. in those areas, where theelectrons from the modulated electron beam land on the storage grid 30,the electrons have sufficient velocity to produce a greater number ofsecondary electrons than incident primary electrons. Thus, moreelectrons leave the storage grid 30 than arrive on these elements of thestorage grid struck by the writing electron beam and the surface 31 ofthe storage grid 30 assumes a less negative charge. The secondaryelectrons emitted from the storage grid are attracted to and collectedby the collector electrode 47. Thus, the storage mesh elements may becharged to any potential intermediate between the storage grid cut offvoltage and zero volts. In this manner, a storage charge pattern iswritten onto the storage grid 30 by the writing gun 50 in accordancewith the modulation applied to the control grid 54 of the writing gun 50from the signal source 57.

In the viewing operation, the viewing gun 60 provides a low velocityelectron beam which floods the storage grid 30. A display with highbrightness and long duration is possible because of the high viewing guncurrent which floods the entire screen during the viewing cycle asopposed to the conventional cathode ray tube where the electron beamexcites any one screen element for less than a microsecond as it scansthe area of the screen. The coating 66 collimates the flooding electronbeam so that the electrons approach the storage grid 30 substantiallynormal to the surface. The collector grid 47 and associated coating 66serve to accelerate the electrons in the viewing beam and to repel anypositive ions which may be generated within the volume between theelectron guns 50 and 60 and the storage grid 30. The potential charge onthe storage layer 31 of the storage grid 30 determines the number ofviewing electrons passing through the apertures in the storage grid Whenthe charge about an aperture in the storage grid 30 is such as to allowpassage of electrons, these electrons are accelerated by means of apositive potential of about 75 volts applied to the suppressor electrode24 and the l0,000 volts applied to the coating 26. These electronspassing through the storage grid 30 then bombard the screen 22 causingthe emission of light therefrom.

In order to appreciate the function and operation of the fieldneutralizing electrode 40 in this reading operation, reference is madeto FIG. 3. Curve 70 shows the brightness built up of an enlarged spot orarea of about three-sixteenths inch diameter versus charge on thestorage grid 30 of a prior art device. Curve 70 indicates that thebrightness built up charge is substantially linear. Curve 72, on theother hand, shows the brightness obtained when the beam is focused sothat the area of charge is about 0.020 inch of a prior art device. Curve72 shows that the brightness obtained does not rise linearly with chargebuilt up and in fact reaches an early saturation in brightness. Theutilization of a field neutralizing electrode 40 as taught by thisinvention results in the curve 72 for a small area spot being modifiedso that its brightness will more closely follow that of curve 70.

In FIG. 4, there is illustrated the field configuration in a prior arttype storage tube wherein the charge is provided on the storage mesh ofabout negative 6 volts on one portion and negative 12 volts on anotherportion. The effect of this field configuration on the electron in theflooding beam is also illustrated. The lateral charge field effectbetween the charge areas extends over several apertures of the storagemesh and substantially reduces possible electron penetration andactually accelerates the electrons laterally. The result is that areduced quantity of electrons will be able to penetrate the storage meshand there is electron dispersion and loss of resolution. The bending ofthe field at the border line between the areas charged to differentvoltages is unavoidable in the prior art devices since the equipotentiallines must converge along this border line in order to comply with thevoltage change.

FIG. 5 illustrates the field configuration in a transmis sion storagetube which utilizes a field neutralizing electrode 40. The equipotentialplane formed by the field neutralizing electrode 40 is placed close tothe storage surface of the storage grid 30 and the field pattern shownin FIG. 4 is modified to that shown in FIG. 5. The field deformationcaused by the non-uniform charge on the storage surface is confined tothe particular mesh or wire of the border line. The field in front ofall the other meshes is undisturbed. The brightness of a small spot willbe the same as that of a large spot. The lateral movement of theelectrons will not exceed one mesh opening. The mesh openings in thestorage grid are about 2 mils and are therefore smaller than the beamthickness of the writing beam. The spot size, therefore, will be thesame as the beam thickness. The field neutralizing mesh 40 should bepositioned as close as possible to the storage surface of the storagegrid 30 in order to limit the field deformation to one mesh opening. Thespacing between the storage grid 30 and the field neutralizing mesh 40should preferably be of the same order of magnitude as the meshopenings. This close spacing requires a high degree of precision instretching the two screens. Actual contact, however,

between the two surfaces poses no problem, since the storage surface 31is a good insulator.

A further improvement or complete elimination of disturbing lateralfield and proximity effects can be obtained by physically merging of theequipotential plane and the storage surface. Such a structure isillustrated in FIG. 6. A storage and neutralizer mesh assembly 73 isshown in which two mesh openings 75 are illustrated.

The storage electrode portion is comprised of an elec trical conductiveback plate mesh 76 with the storage surface 77 provided thereon. Thefield neutralizer electrode portion is provided by depositing aconductive mesh 78 on the storage surface 77 as illustrated. The fieldneutralizer mesh 78 thus surrounds each mesh opening 75 and provides aunipotential surface immediately at the storage surface and prevents thefields from the charges of one mesh opening extending into theneighboring mesh openings. In this manner, complete independence of theindividual mesh openings is secured.

FIG. 7 illustrates another modified storage and separator neutralizerelectrode assembly 79. The assembly 79 comprises a conductive backingelectrode mesh 80. A storage surface 82 is provided and a groove 84 isprovided in the insulating surface 82 and exposes a surface 86 on theconductive storage backing electrode 80. The exposed surface 86 of thebacking electrode provides the equipotential surface. This arrangementis possible since the DC voltage level of the backing electrode may bechosen quite freely and therefore equal to that of the neutralizer mesh.

FIG. 8 illustrates another modification in which a storage, neutralizerand suppressor electrode assembly 93 is provided which comprises abacking electrode mesh 90 of electrical conductive material and astorage surface coating 92 covering the entire mesh 90. The side wallsof the apertures are tapered to expose the side walls to the reading andwriting beam. A field neutralizing electrode 94 is provided on thesurface of the coated mesh facing the electron gun structure and asuppressor electrode 96 provided on the opposite surface of the storagemesh and both electrodes 94 and 96 are insulated from the mesh 90 bymeans of the storage coating 92. In this manner, the three separate gridelectrodes 90, 94 and 96 may be provided in one unitary structure.

Although the present invention has been described with a certain degreeof particularity, it should be un derstood that the present disclosurehas been made only by way of example and numerous changes may beresorted to without departing from the spirit and the scope of theinvention.

I claim:

1. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, an apertured storage gridcomprised of electrical conductive mesh having an insulating coating onat least one surface thereof opposite with respect to said phosphorscreen, a writing electron beam means disposed on the opposite side ofsaid storage grid with respect to said phosphor display screen forgenerating an electron beam and depositing a charge image on saidinsulating coating, a flooding electron beam means also disposed on theopposite side of said storage grid with respect to said phosphor displayscreen for generating and directing electrons through the apertures insaid storage grid and modulated by the charge image thereon intoincidence with said screen, and a field neutralizing electrodepositioned adjacent to said storage grid between said electron beamsources and such storage grid, said field neutralizing electrode havinga plurality of apertures and positioned with respect to said storagemesh so as to restrict the lateral field due to a charge on the storagemesh to substantially each of the individual apertures within saidstorage grid.

2. The tubes set forth in claim 1 in which the apertures in said fieldneutralizing electrode are aligned with the apertures within the storagegrid.

3. The device set forth in claim 2 in which said field neutralizingelectrode is positioned at a distance of less than 0.002 inch from saidinsulating coating on said storage grid.

4. The device set forth in claim I in which said field neutralizingelectrode is positioned on the insulating coating on said storage gridand the apertures in said field neutralizing electrode are aligned withthe apertures in said storage grid.

5. The device set forth in claim 1 in which said insu lating coatingcovers the entire surface of said mesh, said field neutralizingelectrode positioned on the surface of said storage grid facing saidelectron beam sources and the apertures in said storage grid havingtapered sidewalls to provide an aperture at the surface of said storagegrid facing said electron beam sources of a first dimension and anaperture of a second dimension greater than said first dimension at theopposite surface and a suppressor grid provided on the opposite surfaceof said storage mesh with respect to said neutralizing electrode, saidsuppressor grid having a plurality of apertures with the aperturesaligned with the apertures in said storage grid and insulated from theconductive mesh of said storage grid by means of said insulatingcoating.

6. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, a storage grid comprisedof an electrical conducting mesh with an insulating coating provided onat least a portion of said electrical conductive mesh, a writingelectron beam means for depositing a charge image on said insulatingcoating, a flooding electron beam means for generating and directingelectrons through the apertures in said storage grid onto said screen,said flooding beam modulated by the charge image on said storage mesh,said insulating coating covering a portion of the interstices of saidmesh facing said electron beam sources and extending into the aperturesin said mesh such that the insulating coating associated with eachaperture is isolated with respect to the insulating coating of otherapertures and a portion of the electrical conductive mesh between theinsulating coating exposed to said electron beams to provide anequipotcntial grid in substantially the same plane as the insulatingcoating on said storage mesh.

7. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, a combination aperturedgrid electrode provided adjacent said phosphor display screen, a writingelectron beam means for depositing a charge image on said combinationelectrode, a flooding electron beam means for generating and directingelectrons through the apertures in said combination electrode onto saidscreen, said flooding beam modulated by the charge image on saidcombination electrode, said combination electrode comprised of anelectrical conductive mesh, an insulating coating provided over theentire conductive mesh to form an insulated coated apertured grid memberwhose interstices taper to a smaller dimension at the surface facingsaid electron sources, a first electrical conductive coating providedover the surface of said insulated grid facing said electron beam sourceand a second electrical conductive coating provided on the oppositesurface of said insulated grid facing said display screen.

8. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, an apertured storage gridcomprised of electrical conductive mesh having an insulating coating onat least one surface thereof opposite with respect to said phosphorscreen, a writing electron beam means disposed on the opposite side ofsaid storage grid with respect to said phosphor display screen forgenerating an electron beam and depositing a charge image on saidinsulating coating, a flooding electron beam means also disposed on theopposite side of said storage grid with respect to said phosphor displayscreen for gener: ating and directing electrons through the apertures insaid storage grid and modulated by the charge image thereon intoincidence with said screen, and a field neutralizing electrodepositioned on the insulating coating on the side of said storage gridfacing said electron beam sources, said field neutralizing electrodehaving a plurality of apertures thereby aligned with the apertures ofsaid storage grid.

9. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, an apertured storage gridcomprised of electrical conductive mesh having an insulating coatingcovering the entire surface of said mesh, a writing electron beam meansdisposed on the opposite side of said storage grid with respect to saidphosphor display. screen for generating an electron beam and depositinga charge image on said insulating coating, a flooding electron beammeans also disposed on the opposite side of said storage grid withrespect to said phosphor display screen for generating and directingelectrons through the apertures in said storage grid and modulated bythe charge image thereon into incidence with said screen, and a fieldneutralizing electrode positioned on the surface of said storage gridfacing said electron beam sources, and the apertures in said storagegrid having tapered sidewalls to provide an aperture at the surface ofsaid storage grid facing said electron beam sources of a firstdimension, and an aperture of a second dimension greater than said firstdimension at the opposite surface, and a suppressor grid provided on theopposite surface of said storage mesh with respect to said neutralizingelectrode, said suppressor grid having a plurality of apertures with theapertures aligned with the apertures in said storage grid and insulatedfrom the conductive mesh of said storage grid by means of saidinsulating coating.

1. A transmission storage display tube comprising an evacuated envelopeand having therein a phosphor display screen, an apertured storage gridcomprised of electrical conductive mesh having an insulating coating onat least one surface thereof opposite with respect to said phosphorscreen, a writing electron beam means disposed on the opPosite side ofsaid storage grid with respect to said phosphor display screen forgenerating an electron beam and depositing a charge image on saidinsulating coating, a flooding electron beam means also disposed on theopposite side of said storage grid with respect to said phosphor displayscreen for generating and directing electrons through the apertures insaid storage grid and modulated by the charge image thereon intoincidence with said screen, and a field neutralizing electrodepositioned adjacent to said storage grid between said electron beamsources and such storage grid, said field neutralizing electrode havinga plurality of apertures and positioned with respect to said storagemesh so as to restrict the lateral field due to a charge on the storagemesh to substantially each of the individual apertures within saidstorage grid.
 2. The tubes set forth in claim 1 in which the aperturesin said field neutralizing electrode are aligned with the apertureswithin the storage grid.
 3. The device set forth in claim 2 in whichsaid field neutralizing electrode is positioned at a distance of lessthan 0.002 inch from said insulating coating on said storage grid. 4.The device set forth in claim 1 in which said field neutralizingelectrode is positioned on the insulating coating on said storage gridand the apertures in said field neutralizing electrode are aligned withthe apertures in said storage grid.
 5. The device set forth in claim 1in which said insulating coating covers the entire surface of said mesh,said field neutralizing electrode positioned on the surface of saidstorage grid facing said electron beam sources and the apertures in saidstorage grid having tapered sidewalls to provide an aperture at thesurface of said storage grid facing said electron beam sources of afirst dimension and an aperture of a second dimension greater than saidfirst dimension at the opposite surface and a suppressor grid providedon the opposite surface of said storage mesh with respect to saidneutralizing electrode, said suppressor grid having a plurality ofapertures with the apertures aligned with the apertures in said storagegrid and insulated from the conductive mesh of said storage grid bymeans of said insulating coating.
 6. A transmission storage display tubecomprising an evacuated envelope and having therein a phosphor displayscreen, a storage grid comprised of an electrical conducting mesh withan insulating coating provided on at least a portion of said electricalconductive mesh, a writing electron beam means for depositing a chargeimage on said insulating coating, a flooding electron beam means forgenerating and directing electrons through the apertures in said storagegrid onto said screen, said flooding beam modulated by the charge imageon said storage mesh, said insulating coating covering a portion of theinterstices of said mesh facing said electron beam sources and extendinginto the apertures in said mesh such that the insulating coatingassociated with each aperture is isolated with respect to the insulatingcoating of other apertures and a portion of the electrical conductivemesh between the insulating coating exposed to said electron beams toprovide an equipotential grid in substantially the same plane as theinsulating coating on said storage mesh.
 7. A transmission storagedisplay tube comprising an evacuated envelope and having therein aphosphor display screen, a combination apertured grid electrode providedadjacent said phosphor display screen, a writing electron beam means fordepositing a charge image on said combination electrode, a floodingelectron beam means for generating and directing electrons through theapertures in said combination electrode onto said screen, said floodingbeam modulated by the charge image on said combination electrode, saidcombination electrode comprised of an electrical conductive mesh, aninsulating coating provided over the entire conductive mesh to form aninsulated coated apertured grid mEmber whose interstices taper to asmaller dimension at the surface facing said electron sources, a firstelectrical conductive coating provided over the surface of saidinsulated grid facing said electron beam source and a second electricalconductive coating provided on the opposite surface of said insulatedgrid facing said display screen.
 8. A transmission storage display tubecomprising an evacuated envelope and having therein a phosphor displayscreen, an apertured storage grid comprised of electrical conductivemesh having an insulating coating on at least one surface thereofopposite with respect to said phosphor screen, a writing electron beammeans disposed on the opposite side of said storage grid with respect tosaid phosphor display screen for generating an electron beam anddepositing a charge image on said insulating coating, a floodingelectron beam means also disposed on the opposite side of said storagegrid with respect to said phosphor display screen for generating anddirecting electrons through the apertures in said storage grid andmodulated by the charge image thereon into incidence with said screen,and a field neutralizing electrode positioned on the insulating coatingon the side of said storage grid facing said electron beam sources, saidfield neutralizing electrode having a plurality of apertures therebyaligned with the apertures of said storage grid.
 9. A transmissionstorage display tube comprising an evacuated envelope and having thereina phosphor display screen, an apertured storage grid comprised ofelectrical conductive mesh having an insulating coating covering theentire surface of said mesh, a writing electron beam means disposed onthe opposite side of said storage grid with respect to said phosphordisplay screen for generating an electron beam and depositing a chargeimage on said insulating coating, a flooding electron beam means alsodisposed on the opposite side of said storage grid with respect to saidphosphor display screen for generating and directing electrons throughthe apertures in said storage grid and modulated by the charge imagethereon into incidence with said screen, and a field neutralizingelectrode positioned on the surface of said storage grid facing saidelectron beam sources, and the apertures in said storage grid havingtapered sidewalls to provide an aperture at the surface of said storagegrid facing said electron beam sources of a first dimension, and anaperture of a second dimension greater than said first dimension at theopposite surface, and a suppressor grid provided on the opposite surfaceof said storage mesh with respect to said neutralizing electrode, saidsuppressor grid having a plurality of apertures with the aperturesaligned with the apertures in said storage grid and insulated from theconductive mesh of said storage grid by means of said insulatingcoating.